Wrong; this is an invented acronym. MUCK doesn't stand for anything; it was originally created as a tongue-in-cheek parallel to 'MUD', because of course TinyMUCKs are a type of TinyMUD. Likewise, TinyMUSH didn't mean anything.

They're just types of gooey squishy things.

Later, folks who thought they were clever sat around and made up retroactive acronyms for these things such as "Multi-User Created Kingdom" (wrong!) and "Multi-User Shared Hallucination" (also wrong!).

Of course, MUD does mean "Multi-User Dungeon" but a lot of users of tinymuds are irrationally afraid of that etymology.

This is totally wrong. There's no such military term, and someone just made this up. Jurann stupidly stuck this in a "furry dictionary" one time and despite howls of protest from the people who were there at the time, including email from Mav himself, refused to change the entry.

There's no such thing as "mis-appropriated verb" and it doesn't even make sense as to why the military would use such a term, anyway -- nor is there any evidence of this phrase ever being used prior to its invention on muds.